An inkjet printer having a borderless printing function forms an image on the entire surface of a sheet as a recording medium without leaving a margin on the peripheral edge part thereof (for example, JP-A-2001-301201). In this borderless printing, since it is difficult to eject ink drops just on the peripheral edge of a sheet due to a positioning accuracy of the sheet being conveyed, ink drops are ejected in excess to the outside of the sheet so as not to leave a margin on the peripheral edge part of the sheet.
Meanwhile, the ink drops ejected to outside of the sheet are to be deposited on a platen that supports the sheet being conveyed, and thus the deposited ink may stain a sheet to be conveyed next. Since a general platen supports a sheet on upper ends of ribs protruding from a flat plate portion, it is conceivable to increase the amount of protrusion of the ribs so as to prevent side end portions of the sheet from contacting the ink on the flat plate portion of the platen. However, the distance between the flat plate portion of the platen and the sheet increases as the amount of protrusion of the ribs is increased. Accordingly, the flying distance of ink drops ejected to outside of the sheet when ink drops are ejected on the flat plate portion of the platen not on the sheet becomes longer than the flying distance of ink drops when ink drops are ejected on the sheet. Therefore, flying drops becomes more likely to be atomized into mist. Moreover, there is a concern that the ink drops atomized into mist may float without instantly landing to stain the back surface of the sheet and the interior of the printer device.